How many MergeScheduler are there in cluster?

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1

Hi, if this is a common question, please forgive me as a newbie of Elasticsearch.

If I have a ES cluster with 2 nodes and totally I have 10 indexes, each index with 4 shards.
How many MergeScheduler are there in clusers?
That's said a shard is actually a LuceneIndex, does it mean we have 40 MergeScheduler prepared when booting Elasticsearch server?

Or each node has only one MergeScheduler?

2

Have a look at https://www.elastic.co/guide/en/elasticsearch/reference/2.3/index-modules-merge.html

3

I did read this article, but what I like to make sure is, how many "MergeScheduler instance" live in runtime? If MergeScheduler instance is per shard created and live in runtime, that I can expect setting different merge policy and parameters for each index independently. The same question for IndexWriter.

I know each shard is actually a lucene files, but does Elasticsearch controll these shards(files) by using same instance(object) or place each instance per shards?

4

There is a single merge policy for all indices, and it adapts to things.

5

Did you mean that I can't set different merge policy parameters (default is TieredMergePolicy) for each index?

We can only run one setting for all index?

6

Each index has its own merge settings, and every shard of every index has its own instance of e.g. TieredMergePolicy and ConcurrentMergeScheduler since each is a single Lucene index.

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